1. Field of the Invention
The present invention relates to a semiconductor light emitting device such as a light emitting diode (LED).
2. Description of the Related Art
The crystal growth of semiconductor light emitting devices of group III nitride such as GaN has been typically performed using a sapphire substrate. Since the sapphire substrate is not electrically conductive, such semiconductor light emitting devices have been typically configured to take the form of what is called a horizontal semiconductor light emitting device in which an n-electrode and a p-electrode are disposed on the same surface of a semiconductor film. However, recently there have been the establishment of a technique for irradiating the sapphire substrate with a laser beam to strip off the same or a proliferation of an electrically conductive substrate which is mainly made of GaN to be used for growth. It is thus now possible to manufacture what is called a vertical semiconductor light emitting device in which the n-electrode and the p-electrode are provided on the upper surface and the lower surface of the semiconductor film, respectively.
The simplest electrode structure conceivable for the vertical semiconductor light emitting device may be constructed in a manner such that an n-pad-electrode serving as a bonding pad is formed at the center of the surface of an n-type semiconductor layer or a light extraction surface, while a p-electrode is formed generally on the entire area of a p-type semiconductor layer or a mounting surface. However, according to such an electrode structure, current is concentrated immediately below the n-pad-electrode, causing a nonuniform light emission intensity distribution. Furthermore, the current concentration may in turn cause damage to the semiconductor film, degradation in light emission efficiency, and an increase in forward voltage.
In view of the aforementioned problems, a semiconductor light emitting device is disclosed in Patent Literature 1. The semiconductor light emitting device includes a transparent electrode that covers generally the entire area of the surface of an n-type semiconductor layer; an n-pad-electrode provided on the transparent electrode; an auxiliary electrode which is connected to the n-pad-electrode and extends toward the circumferential portion of the transparent electrode; a current blocking layer or an insulator which is located to be opposed to the n-pad-electrode on a surface of a p-type semiconductor layer; and a p-electrode which extends around the current blocking layer on the p-type semiconductor layer. On the other hand, an electrode structure in which two types of electrically conductive layers formed of different materials are disposed side by side on the surface of a semiconductor film is disclosed in Patent Literature 2. Such an electrode structure makes it possible to alleviate current concentration immediately below an n-pad-electrode.
[Patent Literature 1] Japanese Patent Kokai No. 2008-53425
[Patent Literature 2] Japanese Patent Kokai No. 2010-192701